Wellbore cleanout tool and method

ABSTRACT

The present invention is directed to a method and apparatus for cleaning a wellbore. The method is designed to remove debris particles from the wellbore by suspending the debris within the wellbore and then forming an approximately helical flow stream in the wellbore to remove the particles. One apparatus includes a body with a flow channel and multiple nozzles connecting to the flow channel and extending to the circumference of the body. Each nozzle has a nozzle axis that bisects the circumference forming a nozzle axis-circumference intersection; the nozzle axis is not on a plane that is formed by the vertical axis and the nozzle-axis-circumference intersection.

BACKGROUND

The present invention relates generally to an improved method and device for cleaning a wellbore and removing debris therefrom.

Often after drilling or during production of a well, debris such as drill cuttings, sand, proppant, scale, crushed portions of the formation, gun debris, etc. can be generated and collect at the bottom, in the case of non-deviated wellbores, or where the wellbore changes direction, such as in the case of deviated wellbores. Various methods have been used to remove this debris, termed “wellbore cleanout” with limited success. Some operators remove the debris by using a drill bit and associated equipment to disturb the debris by partially drilling into it, and by then dragging the drill bit uphole while maintaining circulation of a cleanout fluid, thereby entraining some of the debris. This dragging of the tool uphole while circulating the cleanout fluid is commonly known as the “sweep cycle.” Such a method has had limited success, typically, as the drill bit itself is poorly designed to disturb the debris and entrainment of the debris in the drilling fluid is mostly ineffective. Further, use of a drilling apparatus for well cleanout is very expensive.

Other operators used a variation of the drill-bit-cleanout method by using a combination of jets to disturb and then entrain the debris. One such method and tool is described in U.S. Pat. No. 6,607,607B2. In this method, the operator disturbs the debris by jetting a fluid through a nozzle downward while the operator is running the tool into the wellbore. Then, when the operator believes a sufficient amount of debris has been disturbed, the operator uses a second jet or set of jets directed upward to entrain the particles of disturbed debris and pulls the tool out of the hole while maintaining a pump rate of cleanout fluid sufficient to maintain the entrainment and remove the disturbed debris particles. This method suffers from a number of problems, particularly acute in deviated wellbores. It is well known that deviated wellbores cause convective debris dropout with such methods, resulting in ineffective debris removal. Convective motion present in convective debris dropout can occur whenever a fluid system is contained by a bottom wall and an upper wall, and at least one wall is not horizontal. In convective debris dropout, as shown in FIGS. 1 a-1 d, particles 20 are shown suspended in a fluid in a deviated portion of wellbore 10, such as when they are disturbed by a fluid jetted downward. Because particles 20 are typically heavier than the fluid in which they are suspended, they move downward within wellbore 10 as shown by particle movement 30 in FIG. 1 b. As shown in FIG. 1 c, a clockwise movement of the fluid depicted by fluid flow arrows 40 begins because of the hydrostatic differences between the upper layer of particles 20 and the lower layer of particles 20, as shown in FIG. 1 c. As particles 20 begin to compact on the lower side of wellbore 10, the sliding of the particles on the lower side of wellbore 10 becomes more pronounced, resulting in a rapid downward slide of particles 20, as shown in FIG. 1 d. As further shown in FIG. 1 d, particle movement 30 is downhole, resulting in a buildup of particles 20 at the lower end of the deviated section of wellbore 10.

Still other operators have attempted to remove debris in a wellbore through the use of a pineapple-type cleaning device such as described in U.S. Pat. Nos. 5,484,016; 5,964,414A1; and 6,059,202A1. In the pineapple device, the tool is comprised of a number of different jets oriented at different angles, much like a pineapple, with some jets facing downwards, some upwards and, often, some sideways. The conventional pineapple-type cleaning device suffers from much the same problems as does the tool described in U.S. Pat. No. 6,607,607B2. In addition, because of the design of the conventional pineapple-type cleaning device, debris particles may be forced down the wellbore or to the sides of the wellbore, resulting in inefficient debris removal. Further, while conventional cleaning tools may have efficiencies of 90% in the laboratory, field efficiencies are often far smaller, often less than 20%.

Improper or inefficient wellbore cleanout has a number of consequences. Multiple trips in the wellbore by the cleanout tool to properly clean the wellbore result in increased well downtime, as well as increased costs. Typically, an improperly cleaned wellbore will require more frequent debris removal, again resulting in increased well downtime and increased costs. In addition, improperly cleaned wellbores may have a reduced production rate, and, in extreme cases, may have a shortened life span. Further, because cleaning fluid removed from the well may appear clear even when substantial debris deposits remain within the wellbore, when using the wellbore cleanout methods previously described, operators may be unaware of the extent or even the existence of such debris. What is needed is a wellbore cleanout tool and method of removing debris from a wellbore that removes debris efficiently and more effectively than conventional methods.

SUMMARY

The present invention is directed to a device and method for effectively cleaning a wellbore.

More specifically, one embodiment of the present invention is directed to a method of removing debris from a wellbore, the wellbore having a wellbore axis and a sidewall, by suspending the debris particles in a fluid to form suspended particles, forming an approximately helical flow stream in the wellbore about an axis of rotation, wherein the axis of rotation is generally parallel to the wellbore axis, and removing the debris particles from the wellbore.

Another embodiment of the present invention is directed to a wellbore cleanout tool that includes a generally cylindrical body having a flow channel therethrough, a vertical axis, a top surface plane, and a circumference and a plurality of nozzles mechanically connecting to the flow channel and further extending to the circumference. Each nozzle has a nozzle axis that bisects the circumference forming a nozzle axis-circumference intersection. The nozzle axis is not on a plane formed by the vertical axis and the nozzle axis circumference.

Still another embodiment of the present invention is directed to a method of cleaning debris from a wellbore, the wellbore having a sidewall, by providing a wellbore cleanout tool having a generally cylindrical body having a flow channel therethrough, a vertical axis, a top surface plane, and a circumference, a plurality of nozzles mechanically connecting to the flow channel and further extending to the circumference, wherein each nozzle has a nozzle axis that bisects the circumference forming a nozzle axis-circumference intersection, wherein the nozzle axis is not on a plane formed by the vertical axis and the nozzle axis-circumference intersection, and a bottom orifice, the bottom orifice mechanically connected to the flow channel. The wellbore cleanout tool is lowered into the wellbore and a cleanout fluid is flowed through the bottom orifice to form debris particles. The wellbore cleanout tool is then raised in the wellbore while jetting the cleanout fluid through the nozzles.

Yet another embodiment of the present invention is directed toward a wellbore cleanout tool having a generally cylindrical center member. The generally cylindrical center member has an outer surface, a fluid inlet, a fluid outlet, and a center flow channel therethrough connecting the fluid inlet and fluid outlet. The wellbore cleanout tool further includes a helical vane mechanically attached to the outer surface.

Another embodiment of the present invention is directed toward a method of cleaning debris from a wellbore with the wellbore having a wellbore axis. The steps include providing a wellbore cleanout tool having a generally cylindrical center member having an outer surface, a fluid outlet, and a helical vane mechanically attached to the outer surface, lowering the wellbore cleanout tool in the wellbore, and flowing a fluid through the fluid outlet. The debris particles are suspended in the fluid and a helical flow pattern is formed in the fluid along the wellbore axis.

The features and advantages of the present invention will be readily apparent to those skilled in the art upon a reading of the description of the exemplary embodiments, which follows.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete understanding of the present disclosure and advantages thereof may be acquired by referring to the following description taken in conjunction with the accompanying drawings:

FIGS. 1 a-1 d are a series of schematics depicting the effect of deviated wellbores on particle fall rate.

FIG. 2 is cutaway view of one embodiment of a wellbore cleanout tool according to the present invention.

FIG. 3 is a side view of one embodiment of a wellbore cleanout tool according to the present invention.

FIG. 4 is an expanded view along cutline 4 of FIG. 3 depicting nozzle orientation of one embodiment of a wellbore cleanout tool according to the present invention.

FIG. 5 is side view of one embodiment of a wellbore cleanout tool according to the present invention.

FIG. 6 is a top view of one embodiment of a wellbore cleanout tool according to the present invention.

FIG. 7 is a graph illustrating the efficiency of removal in a 45 degree deviated wellbore.

FIG. 8 is a graph illustrating the interrelationship between the angle of a nozzle of a wellbore cleanout tool and the required jet pressure.

DETAILED DESCRIPTION

The details of certain embodiments of the present invention will now be described with reference to the accompanying drawings. One embodiment of the present invention is directed to a method of removing debris particles from a wellbore, in part, through the use of a Bernoulli effect. This effect is described by Bernoulli's law and is equivalent to lift commonly associated with flight. For systems subject to the Bernoulli effect, an increase in the velocity of horizontal fluid flow will result in a decrease in the static pressure. In certain embodiments of the present invention, debris particles within the wellbore are entrained in a high-velocity fluid stream with a vector perpendicular to the wellbore axis, termed the “horizontal flow rate”. Because the wellbore may be, and often is, deviated, the horizontal flow itself may be only nominally “horizontal.” Any horizontal flow rate is normally circular based on the characteristics of the wellbore itself and is about an axis of rotation that is generally parallel to the wellbore axis. It is preferable that the axis of rotation be approximately coincident with the wellbore axis itself, facilitating removal of the debris particles, although depending on the wellbore configuration, a coincident wellbore axis and axis of rotation may not be possible.

As debris particles enter the fluid stream, the debris particles are accelerated until their velocity equals that of the fluid stream. When these particles reach such a velocity, because of conservation of momentum and the widening of the fluid stream, the fluid stream decreases in velocity. Because the debris particles are then moving faster than the fluid stream, they are effectively “slung” or lifted by fluid along the axis of the wellbore and towards the surface in a helical flow pattern. By moving the debris particles in this generally helical flow pattern or stream, the debris particles can be removed from the wellbore. This slinging action may be further improved through the use of differential velocity. Typically, initially, the wellbore contains a large volume of stagnant fluid. The helical flow pattern may be initiated by introducing a high-velocity fluid into the wellbore. As the high-velocity fluid stream enters the wellbore, the high-velocity fluid stream encounters the stagnant fluid. The energy of the high-velocity fluid stream is most often divided almost evenly between all fluid and debris within the wellbore. Typically, the stagnant fluid within the wellbore contains a much higher fluid volume than is introduced into the wellbore through the high-velocity fluid stream. As a result, the mixture of the high-velocity fluid stream and the initially stagnant fluid within the wellbore will have a lower fluid velocity than the fluid stream introduced into the wellbore, as determined by the following equation: E _(m) =M _(m) V _(m) ²/2=M _(hv) V _(hv) ²/2+M _(s) V _(s) ²/2

where subscript m refers to the resultant mixture of fluids, subscript hv the high-velocity fluid and subscript s the stagnant fluid. From a review of this equation, it is evident that because the mass of the mixture is high compared to that of the high-velocity fluid the mixture velocity would be lower. This difference in velocities between the high-velocity fluid and the mixture improves the slinging effect and improves the particle transport process.

The amount of slinging action imparted by fluid stream is dependent upon the horizontal flow rate and the density difference between the debris particles and the fluid. Debris particle size and shape also have an effect on the slinging action. The larger the horizontal flow rate and the larger the density difference between the debris particles and the cleanout fluid, the greater the slinging action. However, the larger the density difference between the debris particles and the fluid, the greater the dropout effect. One of ordinary skill in the art will appreciate that the trade-off between the increase in the slinging effect with the increased dropout effect can be optimized based on the particular debris particle density and fluid used.

A horizontal velocity alone may be insufficient to propel debris particles to the surface. Hence, in at least some embodiments of the present invention, the fluid stream must have, in addition to a vector perpendicular to the axis of the wellbore, a vector along the axis of the wellbore, termed a “vertical flow rate.” This vertical flow rate will be directed towards the surface. The vertical flow rate, in conjunction with the horizontal flow rate, provides the impetus to propel the debris particles to the surface for removal. The slinging action described above contributes to the placement of debris particles ahead or above the high-velocity stream.

Once the particles are slung upwards, upward fluid movement will tend to carry the particles upward. However, if, as in most cases, the particles are heavier than the fluid, then there will be a relatively slow drop of the particles downward, i.e., the “dropout effect.” This particle movement can be defined as a passing or conduction-type movement, as gravitational forces draws the particle through the fluid. This type movement can generally be negated by some upward fluid flow. When the wellbore is vertical, normally a small flow rate of fluid upward is all that is required to counteract this conduction-type movement. If the wellbore is horizontal, the flow rate of fluid upward may need to be higher to create turbulence to counteract this conductive movement. Typically, the introduction of the cleanout fluid creates such turbulence and the conductive motion in the horizontal section of the wellbore is generally overcome by such turbulence. Further, a viscous cleanout fluid may be used to reduce conductive motion. However, transitions between horizontal and vertical wellbore are typically accomplished through the use of deviated sections of a wellbore and, in fact, wellbores are deliberately deviated. As described above and shown in FIGS. 1 a-1 d, in deviated wells, the downward gravitational pull will cause particles to move towards the lower side of the wellbore. Even a small movement in particles downward will cause a large imbalance of the hydrostatic forces on the upper side of the wellbore as compared to the lower side of the wellbore. The heavier fluid mixture will rapidly flow downwards on the lower side, while the lighter mixture flows upwards on the upper side. Shear forces between the upper portion of the upper side and the lower portion of the lower side create a circulatory motion that further pulls heavy particles downwards. Hydrostatic imbalances increase rapidly, increasing dropout velocity, increasing shear and thereby increasing particle dropout. As the downward flow reaches a lower section, at some point it will circulate back upwards, slinging the heavier particles downwards. This phenomenon is often referred to as “convective motion.” As convective movement is usually very fast, flow rates to counteract this fall must be quite large. The convective motion may force the particles downward and result in agglomeration of the particles, i.e., “packing,” causing difficulties for moving equipment, or “sticking.” It is this convection motion that the helical motion of the fluid will counteract in some embodiments of the invention.

Forcing the fluid to move in a helical motion counteracts downward particle movement and causes a continuous mix. As one of ordinary skill in the art will appreciate, the rotational velocity of this helical motion is most efficient within a certain range. For instance, excessively high rotational velocities result in a decreased efficiency of particle removal as it compacts debris particles at the perimeter of the helical flow. This compaction results in a substantial hydrostatic difference for even a minute change in debris particle positioning. As is illustrated by FIG. 7 for a wellbore deviated at 45°, the cleaning efficiency, i.e., the percentage of total debris in the wellbore removed, rises with increased rotational speed until it reaches a maximum efficiency. Thereafter, with increased rotational speed, the cleaning efficiency falls. The rotational velocity associated with maximum efficiency for a given set of circumstances is termed the “optimal rotational velocity.” The optimum rotational velocity depends upon on a number of factors including the wellbore structure, the fluid type, the fluid condition, and the intended sweep rate. Wellbore structure is at least a combination of the wellbore deviation and diameter, and the annulus between any tool inserted into the wellbore wall. Generally, as wellbore deviation and diameter increase, the optimum rotational velocity also tends to increase. Similarly, as the annulus between any tool inserted into the wellbore and the wellbore wall increases, the optimum rotational velocity increases. The fluid type and the fluid condition is a combination of the actual fluid type used for wellbore debris removal and the reaction of that fluid within the wellbore. Examples include, but are not limited to, viscosity and the effect on viscosity caused by shear, temperature and pressure, and density, and the effect of density on temperature and pressure. Typically, the further the density of the fluid is from the density of the debris particles to be removed, the more the optimum rotational velocity increases. A more viscous fluid may tend to decrease the need for a high optimum rotational velocity. Intended sweep rate is simply the rate at which any device used to impart the rotational velocity to the fluid is withdrawn from the wellbore. The higher the intended sweep rate, typically the higher the optimum rotational velocity. As will be recognized by one of ordinary skill in the art, the factors outlined tend to work in concert, i.e., a high intended sweep rate and a small annulus may partially offset each other on the effect of the optimum rotational velocity.

Changes in these factors have the effect of shifting and changing the shape of the curve shown in FIG. 7, thereby changing the optimum rotational velocity. Persons of ordinary skill in the art will recognize that it is most often desirable to operate as close to the optimum rotational velocity as is possible in order to maximize debris removal and minimize downtime of the well associated with cleaning. Generally, at least some of the factors associated with the optimum rotational velocity are known. The operator will, in most cases, attempt to control the rotational velocity as close to the optimum rotational velocity in order to maximize cleaning efficiency of the wellbore or wellbore section to be cleaned. While certain conditions may limit the ability of the operator to operate at the optimum rotational velocity, such as a maximum pressure limitation on the high-velocity fluid, typically, the rotational velocity should generally be controlled as to effect at least an 85% cleaning efficiency in actual operation, preferably more than 90%, more preferably in excess of 95% cleaning efficiency, and most preferably remove substantially all of the debris particles.

In certain embodiments of the present invention, it may be desirable prior to lifting and removing the debris particles to break up or break apart debris in the wellbore to form debris particles and suspend those debris particles in a fluid. Hence, in certain embodiments of the present invention, the fluid flow may have a vector along the axis of the wellbore opposite the vertical flow rate, termed a “downward flow rate.”

In other embodiments of the present invention, it may be desirable to “scrub” or remove debris particles that may adhere to the sidewall of the wellbore. In those situations, fluid may also be directed to the wellbore sidewall. Typically, such flow must be adequate to both break up and remove the debris particles adhering to the wellbore sidewall, as well as to thereafter suspend such debris particles in the fluid.

A variety of fluids may be used to remove debris particles from the wellbore, which should be selected based on a number of variables. First, the fluid should be selected based on its ability to support the debris particles. The closer the density of the fluid to the debris particles, the better able the fluid is to support those debris particles. Lighter-weight fluids may result in debris settling caused by convection, as described previously. Further, it is desirable that the fluid be a low-friction at high-stress fluid, thereby minimizing drag at the conditions typically present during wellbore cleanout. Some examples of fluids that may be so used include fluids typically used as fracturing fluids, such as water, including water containing a salt such as NaCl, CaCl, CaBr ZnBr or NH₄Cl together with Xanthant Biopolymer or Liquid HEC Polymer.

The cleanout fluid may contain additives and other agents designed to mitigate or otherwise alter the effect of the cleanout fluid on the formation or the debris particles. For instance, a fluid loss component, such as nitrogen foamed with the fluid, may be included with the cleanout fluid. Any fluid loss component added to the fluid should generally not act to cause fractures in the well and that the fluid loss component not so change the density of the cleanout fluid as to present unacceptable debris settling by convection. When using nitrogen to create a foam, it may be desirable to include a foaming agent to create a better quality foam. Unfortunately, the use of nitrogen may also cause lowering of the fluid density, which, as may result in higher convective motion. Further, low quality foams tend to separate quickly, while very high quality foams tend to be more stable. Though density of the high quality foam is typically less, its stability may demonstrate benefits greater than the higher density, low quality foams in counteracting convective flow.

Turning to FIG. 2, one embodiment of a wellbore cleanout tool for use in accordance with the present invention is shown generally by reference numeral 100. Nozzle-type wellbore cleanout tool 100 includes a generally cylindrical body 110, which has flow channel 120 extending therethrough. Typically, generally cylindrical body 110 includes circumference 112, inner surface 114, top surface plane 116, and outer surface 118. Inner surface 114 circumscribes flow channel 120. In the embodiment of the present invention depicted in FIG. 2, generally cylindrical body 110 is comprised of four primary sections: lower body 130; shoulder 140; throat 150; and upper body 160. In the embodiment depicted in FIG. 2, flow channel 120 extends through lower body 130 and terminates in lower orifice 132. Lower orifice 132 should be designed to disturb or break apart any debris it encounters and provide fluid in order to suspend the disturbed debris. Typically, lower orifice 132 is of smaller diameter than flow channel 120, although the diameter of lower orifice 132 may depend on particular wellbore and fluid conditions. By reducing the diameter of lower orifice 132 from the diameter of flow channel 120, it is possible to increase the pressure of the any fluid that flow through lower orifice 132 to provide additional assistance in disturbing and breaking up any debris. In other embodiments of the present invention, lower orifice 132 is not included and flow channel 120 does not have an outlet through lower body 130. In the embodiment depicted in FIG. 2, lower body 130 tapers to reduce the cross-sectional area of lower orifice 132 from the cross-sectional area of the section of flow channel 120 within lower body 130. In addition, while one lower orifice 132 is depicted in FIG. 2, a plurality of lower orifices 132 may be used in other embodiments. Further, while lower orifice 132 is shown in FIG. 2 to be directed in a single direction along vertical axis 220, lower orifice 132 may also have a horizontal component as well. As one of ordinary skill in the art will appreciate, by determining the degree of taper of lower body 130, it is possible to control, in part, the pressure of fluid flows through lower orifice 132.

As further shown in FIG. 2, shoulder 140 of generally cylindrical body 110 is located proximate to lower body 130. Shoulder 140 is tapered to provide a transition between lower body 130 and throat 150 and angled so as present the proper angles for nozzles 146. Nozzles 146 provide a passageway between inner surface 114 and outer surface 118 of generally cylindrical body 110, allowing fluid communication between flow channel 120 and nozzle orifice 142. Nozzles 146 each have nozzle axis 144. Each nozzle axis 144 bisects circumference 112 at nozzle axis-circumference intersection 148. In the present invention, each nozzle axis 144 is not on a plane that is formed between vertical axis 220 and nozzle-axis-circumference intersection 148. By placing nozzle orifice 142 such that nozzle axes 144 are so positioned, fluid exiting nozzle orifice 142 acts to create the horizontal flow rotation described above. In the embodiment of the present invention depicted in FIG. 2, each nozzle axis 144 is at an acute angle to vertical axis 220; the angle between each nozzle axis 144 and vertical axis 220 need not be identical. Further, in the embodiment of the invention depicted in FIG. 2, each nozzle axis 144, if extended, would bisect top surface plane 116. In other embodiments of the present invention, each nozzle axis 144 is at an angle perpendicular to the vertical axis.

The angle of the nozzle may be an important consideration in the design of nozzle-type wellbore cleanout tool 100. FIG. 8 describes the interrelationship between the pressure necessary to remove debris from the wellbore and the angle between each nozzle axis 144 and vertical axis 220 for various casing sizes and wellbore deviations. As is shown in FIG. 8, generally increasing the angle between each nozzle axis 144 and vertical axis 220 will decrease the amount of jet pressure necessary to remove debris from the wellbore. FIG. 8 also shows that for a given jet angle and casing size, changing the deviation of the wellbore from a 58° deviation to a 45° deviation requires an increase in pressure through nozzles 146.

Typically, nozzle-type wellbore cleanout tool 100 comprises between 2 and 100 nozzles 146, although more or fewer nozzles 146 may be used, depending upon the size of nozzle-type wellbore cleanout tool 100. FIG. 4 further depicts the orientation of nozzles 146.

In the embodiment of the present invention depicted in FIG. 2, nozzles 146 terminate at outer surface 118 of generally cylindrical body 110. In certain embodiments of the present invention, nozzles 146 may protrude beyond outer surface 118. In certain embodiments where nozzles 146 protrude beyond outer surface 118, throat 150 may be eliminated and shoulder 140 may not taper. Throat 150 where present, is proximate to and tapers to upper body 160. Upper body 160 is typically designed to receive connecting piping, such as coiled tubing, although any method of connection may be used such as threading, welding, or pressing.

In certain embodiments of the present invention, as shown in FIG. 3, flats 170 are shown on the outer surface 118 of generally cylindrical body 110. Flats 170 are typically machined from outer surface 118 of generally cylindrical body 110. Flats 170 are designed to allow connection of other tools to generally cylindrical body 110 or to manipulate generally cylindrical body 110 in wellbore 10. FIG. 4 provides an edge-on view of nozzles 146.

In the embodiment of the present invention depicted in FIG. 2, a single row of nozzles 146 are shown. Other configurations are possible, including, but not limited to, a double row of nozzles 146.

In one embodiment of the present invention, nozzle-type wellbore cleanout tool 100 is designed to break up debris present in the wellbore, clean the casing wall, and to remove the debris from the wellbore. Fluid is introduced into nozzle-type wellbore cleanout tool 100 through flow channel 120. In certain embodiments employing lower orifice 132, fluid passes through lower orifice 132. Such fluid acts to replace any fluid loss into the well that may be experienced either by removal with debris at the top of the well, or through fluid loss into the well itself during the wellbore cleaning operation. If more fluid is lost to the formation and/or removed at the surface than is replaced during the wellbore cleaning operation, the fluid may experience a downward movement. By reducing fluid loss, debris resettling is minimized because of downward fluid movement. In addition, fluid passing through lower orifice 132 may be used to break up and/or disturb the debris within the wellbore forming debris particles. Further, fluid passing through lower orifice 132 typically acts to suspend the debris particles so formed.

Nozzles 146 may act by jetting fluid to create turbulence in order to initiate mixing of the debris and the fluid, to contribute towards an upward vector of the fluid, to create an upward Bernoulli effect for moving debris towards the top of the well, to create a slinging action for moving debris towards the top of the well, and/or to promote rotary action to combat any convective particle dropping as depicted in FIGS. 1 a-1 d. Hence, nozzles 146 form the helical effect described previously.

This vertical vector component of fluid leaving nozzles 146 has the ability to propel debris toward the top of the well. In addition, nozzles 146 may act to create a Bernoulli effect to further increase uphole mobility of debris particles. For systems subject to the Bernoulli effect, an increase in the velocity of horizontal fluid flow will result in a decrease in the static pressure. In essence, fluid jetted through nozzles 146 acts to move the particles upward through the Bernoulli effect. This effect is described by Bernoulli's law as described previously.

As one of ordinary skill in the art will recognize, it is possible to vary the horizontal flow rate around the tool by varying the pressure of the fluid jetted through nozzles 146, the size of nozzle orifices 142, the size of lower orifice 132, or the number of nozzles 146. The Bernoulli effect may be reduced in large boreholes and an increase in horizontal flow rate may be necessary to counteract this effect. The horizontal velocity may also be impacted by the angle between nozzle axis 144 and vertical axis 220. Decreasing the angle between vertical axis 220 and nozzle axis 144 decreases the horizontal flow rate.

The amount of slinging action imparted by nozzles 146 is dependent upon the horizontal flow rate and the density difference between the debris particles and the fluid. Debris particle size and shape also have an effect on the slinging action. The larger the horizontal flow rate and the larger the density difference between the debris particles and the cleanout fluid, the greater the slinging action. However, the larger the density difference between the debris particles and the cleanout fluid, the greater the convection dropout effect. Further, in order to prevent further fracture of the formation surrounding the wellbore, the pressures of cleanout fluid exiting nozzles 146 should generally be kept under 2000 psi, although this value will depend on the formation surrounding the wellbore. Thus, one of ordinary skill in the art can adapt the horizontal flow rate and the fluid type in order to meet his particular wellbore debris situation.

In certain embodiments of the present invention, nozzle-type wellbore cleanout tool 100 and a fluid may be used to remove debris from wellbores. Nozzle-type wellbore cleanout tool 100 is typically attached to some form of flexible piping such as coiled tubing. Nozzle-type wellbore cleanout tool 100 is lowered to reach the debris in the wellbore. A fluid is then introduced into the wellbore through lower orifice 132 and nozzles 146. As the fluid is jetted through lower orifice 132, the debris is disturbed and may be broken into smaller particles. The action of the fluid through lower orifice 132 typically causes a suspension of the debris particles in the cleanout fluid. Nozzle-type wellbore cleanout tool 100 may then be lowered as debris is suspended in the cleanout fluid. While nozzle-type wellbore cleanout tool 100 is lowered, fluid jetted through nozzles 146 may also act to clean the sides of the wellbore.

As nozzle-type wellbore cleanout tool 100 is lowered, fluid jetted through nozzles 146 act to form a helical flow pattern with entrained debris particles within at least a section of the wellbore. Typically, this helical flow pattern will not reach the surface of the wellbore, although in certain circumstances, there will be a rotational velocity to the surface exiting fluid. Fluid with entrained debris particles that reaches the surface of wellbore 10 is removed and may be filtered and recycled through nozzle-type wellbore cleanout tool 100. Any fluid loss through such removal is typically replaced through fluid exiting lower orifice 132. At a desired time, such as when the operator believes all or a sufficient amount of debris in the wellbore has been disturbed and suspended or the bottom of the wellbore is reached, nozzle-type wellbore cleanout tool 100 is withdrawn from the wellbore. Nozzles 146 act to create turbulence in order to facilitate mixing of the debris and the fluid, to contribute towards an upward vector of the fluid, to create an upward Bernoulli effect for moving debris towards the top of the well, to create a slinging action for moving debris towards the top of the well, and/or to promote rotary action to combat any convective particle dropping as depicted in FIGS. 1 a-1 d. The speed at which nozzle-type wellbore cleanout tool 100 is withdrawn and should be selected so as to minimize the amount of downtime the well experiences as a result of the cleanout process, but not so quickly as to cause particles to drop out of the fluid being jetted from nozzles 146. Further, as described above, increasing the speed at which nozzle-type wellbore cleanout tool 100 is removed may require a higher rotational velocity. As typically, the rotational velocity is increased by increasing the pressure of the fluid entering flow channel 120, generally, care should be taken not to select a removal rate of wellbore cleanout tool 100 so high as to require a fluid pressure in excess of the fracture pressure of the formation. It may be necessary, depending on the condition of the wellbore and the amount of debris within to lower and raise wellbore cleaning tool multiple times to accomplish complete cleaning of the wellbore.

In another embodiment of the present invention, depicted in FIGS. 5 and 6, another embodiment of a wellbore cleanout tool is depicted. Vane-type wellbore cleanout tool 400 includes generally cylindrical center member 410. Generally cylindrical center member 410 includes fluid inlet 420, center flow channel 430, and fluid outlet 440. Fluid inlet 420 is generally designed to be adapted to piping such as coiled tubing. Fluid outlet 440 may have a diameter equal in size to center flow channel 430, or may be tapered to a smaller diameter. Center flow channel 430 acts to conduct fluid through generally cylindrical center member 410 between fluid inlet 420 and fluid outlet 440. At least one helical vane 460 is attached to the vane-type wellbore cleanout tool outer surface 450 of generally cylindrical center member 410, although, as shown in FIGS. 5 and 6, generally a plurality of helical vanes 460 are used.

During operation, fluid is introduced into center flow channel 430 of vane-type wellbore cleanout tool 400 through fluid inlet 420. Fluid travels through center flow channel 430 and exits vane-type wellbore cleanout tool 400 through fluid outlet 440. Fluid exiting through fluid outlet 430 acts to break up and suspend debris particles within wellbore 10. The fluid then travels within wellbore 10 around the at least one helical vane 460, imparting a generally helical flow pattern to the rising fluid and suspended debris particles. In this way, the rotational flow described previously is imparted to the fluid and suspended particles and the particles may be removed from wellbore 10.

Therefore, the present invention is well-adapted to carry out the objects and attain the ends and advantages mentioned as well as those which are inherent therein. While the invention has been depicted, described, and is defined by reference to exemplary embodiments of the invention, such a reference does not imply a limitation on the invention, and no such limitation is to be inferred. The invention is capable of considerable modification, alteration, and equivalents in form and function, as will occur to those ordinarily skilled in the pertinent arts and having the benefit of this disclosure. The depicted and described embodiments of the invention are exemplary only, and are not exhaustive of the scope of the invention. Consequently, the invention is intended to be limited only by the spirit and scope of the appended claims, giving full cognizance to equivalents in all respects. 

1. A method of removing debris particles from a wellbore section, wherein the wellbore has a wellbore axis and a sidewall, comprising the steps of: (a) suspending the debris particles in a fluid to form suspended debris particles; (b) forming an approximately helical flow stream in at least part of the wellbore section about an axis of rotation, wherein the axis of rotation is generally parallel to the wellbore axis and further, wherein the helical flow stream has a rotational velocity; and (c) removing the suspended debris particles from the wellbore.
 2. The method of claim 1 wherein the rotational velocity is controlled so as to achieve at least 85% removal of the suspended debris particles from the wellbore section.
 3. The method of claim 2 wherein the rotational velocity is controlled so as to achieve at least 90% removal of the suspended debris particles from the wellbore section.
 4. The method of claim 3 wherein the rotational velocity is controlled so as to achieve at least 95% removal of the suspended debris particles from the wellbore section.
 5. The method of claim 4 wherein the rotational velocity is controlled so as to remove substantially all of the suspended debris particles in the wellbore section.
 6. The method of claim 1 wherein the helical flow stream is formed by jetting a high pressure fluid through a nozzle.
 7. The method of claim 1 wherein the axis of rotation is approximately coincident with the wellbore axis.
 8. The method of claim 1 further comprising after step (a) the step of imparting a velocity generally parallel to the wellbore axis to the suspended debris particles.
 9. The method of claim 1 further comprising following step (a) the step of impelling the fluid against the sidewall of the wellbore.
 10. The method of claim 1 wherein the fluid comprises water.
 11. The method of claim 10 wherein the fluid further comprises NaCl, CaCl, CaBr ZnBr or NH₄Cl.
 12. The method of claim 10 wherein the fluid further comprises Xanthan Biopolymer or Liquid HEC Polymer.
 13. The method of claim 10 wherein the fluid further comprises a nitrogen foam.
 14. The method of claim 13 wherein the fluid further comprises a foaming agent.
 15. A wellbore cleanout tool comprising: a generally cylindrical body having a flow channel therethrough, a vertical axis, a top surface plane, an outer surface, and a circumference; and a plurality of nozzles connecting to the flow channel and further extending to the circumference, wherein each nozzle has a nozzle axis that bisects the circumference forming a nozzle axis-circumference intersection, and the nozzle axis is not on a plane that is formed by the vertical axis and the nozzle-axis-circumference intersection.
 16. The wellbore cleanout tool of claim 15 wherein the nozzle axis of each nozzle is at an angle perpendicular to the vertical axis of the generally cylindrical body.
 17. The wellbore cleanout tool of claim 15 wherein the nozzle axis of at least one nozzle is at an acute angle to the vertical axis, and the nozzle axis of at least one nozzle bisects the top surface plane.
 18. The wellbore cleanout tool of claim 15 wherein the nozzles comprise between 2 and 100 nozzles.
 19. The wellbore cleanout tool of claim 15 wherein the nozzles protrude beyond the outer surface.
 20. The wellbore cleanout tool of claim 15 wherein the wellbore cleanout tool is capable of connection to a coiled tubing.
 21. The wellbore cleanout tool of claim 15 further comprising a bottom orifice connected to the flow channel.
 22. The wellbore cleanout tool of claim 15 wherein the nozzles are arranged in at least one row of nozzles.
 23. The wellbore cleanout tool of claim 22 wherein the row of nozzles is perpendicular to the vertical axis.
 24. The wellbore cleanout tool of claim 15 wherein the nozzles are arranged in at least two row of nozzles, and each row of nozzles is perpendicular to the vertical axis.
 25. A method of cleaning debris from a wellbore having a sidewall, comprising: (a) providing a wellbore cleanout tool comprising: a body having a flow channel therethrough, a vertical axis, a top surface plane, and a circumference; a plurality of nozzles connecting to the flow channel and further extending to the circumference, wherein each nozzle has a nozzle axis that bisects the circumference forming a nozzle axis-circumference intersection, and the nozzle axis is not on a plane that is formed by the vertical axis and the nozzle-axis-circumference intersection; and a bottom orifice connected to the flow channel; (b) lowering the wellbore cleanout tool in the wellbore; (c) flowing a fluid through the bottom orifice to form debris particles; and (d) raising the wellbore cleanout tool in the wellbore while jetting the fluid through the nozzles.
 26. The method of claim 25 wherein pressure of the fluid flowed through the bottom orifice is less than 2000 psig.
 27. The method of claim 25 wherein pressure of the fluid jetted through the nozzles is less than 2000 psig.
 28. The method of claim 25 further comprising suspending the debris particles in the fluid.
 29. The method of claim 25 further comprising imparting a horizontal velocity to the fluid to induce lift on the debris particles.
 30. The method of claim 29 further comprising imparting a vertical velocity on the fluid.
 31. A wellbore cleanout tool comprising: a member having an outer surface, a fluid inlet, a fluid outlet, and a flow channel therethrough connecting the fluid inlet and fluid outlet; and a helical vane mechanically attached to the outer surface.
 32. The wellbore cleanout tool of claim 31 further comprising a plurality of helical vanes.
 33. A method of cleaning debris from a wellbore having a wellbore axis, comprising: (a) providing a wellbore cleanout tool having an outer surface, a fluid outlet, and a helical vane attached to the outer surface; (b) lowering the wellbore cleanout tool in the wellbore; (c) flowing a fluid through the fluid outlet; (d) suspending debris particles in the fluid; and (e) forming a helical flow pattern in the fluid along the wellbore axis. 